As regards "confusing" the Constitution
classes, the idea of the Constellation
, NCC-1017, being a prototype or early model for the Constitution
class is perfectly valid in terms of canon. At least if we believe in batch registries, in which case 1017 is likely to have been preceded by something more "round". Perhaps the forefather USS Constitution
was NCC-1000, or perhaps 1010?
The thing is, the later fan/backstage identity of USS Constitution
as NCC-1700 is fuzzy enough to allow for this. All we ever see is a ship of the TMP configuration with this registry but no name in one early TNG graphic, after all.
In any case, using a vessel from one class as a prototype for another is common practice in Star Trek fanfic - especially the Miranda
class (by its various fanfic names) is claimed to descend from prototype vessels modified from very different-looking classes, such as FASA's Anton
or the Mastercom/SotSF Detroyat
. It just happens extremely seldom in the real world because ships are too big to be "prototyped": if you build it, you make it operational, or you go bankrupt. (The recent "Littoral Combat Ship" USN corvettes are a notable exception, and their half-baked nature has caused a lot of confusion and debate in a government that thought it was funding actual operational warships.)
The "by configuration, a starship" phrase can mean a lot of things. If one were to say "by configuration, a battleship" in the early to mid 20th century context, one would be commenting on easily identifiable things such as turreted large-caliber main guns. "By configuration, a cruiser" would be pretty clear as well. We don't know if Spock's definition would have covered something like the Miranda
class, but if he can merely state a "configuration" rather than exact identity, then it's likely that the definition would at the very least cover a wide range of two-hulled two-nacellers in the appropriate size.